"Could not find a valid gem in any repository" (rubygame and others)

Check if you have "https://rubygems.org/" as a source to find gems at:

$ gem sources*** CURRENT SOURCES ***https://rubygems.org/

If not, you should be able to add it with

$ gem sources --add https://rubygems.org/https://rubygems.org/ added to sources

Here are docs for the gem source command.

ruby gem rubygame

You can also add the source you want on the command whenever you have troubles using https, like this:

gem install GEMNAME --source http://rubygems.org

It's better to fix the SSL problem though.

ruby gem rubygame

are you behind any proxy?

check your browser for proxy that you might use:

execute the command: gem install xxx --http-proxy=http://user:password@server and you should be good to go.

CodeHunter